Publications (16)11.04 Total impact

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A millimeter-wave passive Van Atta retrodirective antenna (RDA) array is presented in substrate integrated waveguide technology. The proposed RDA design is based on alternating SIW slot antenna arrays whose longitudinal slots are etched in a continuous ground plane covering the entire circuit thus minimizing the diffraction at the edges of the feeding network. Owing to its closed guiding medium and high Q factor, the SIW feed topology provides an optimum coupling to the radiating elements with minimum losses and spurious feed radiation allowing a simple passive design with enhanced radar cross section (RCS). Two SIW-based prototypes are presented in both single- and double-layer configurations at 30 GHz. While the single layer design can be extended to larger RDAs with minimum losses, the double-layer configuration is exploited to provide a more compact design that reduces the scattering of the structure while providing the same re-radiated pattern of the corresponding single layer configuration. Simulated and measured results are in good agreement showing more than 10 dB enhancement in the monostatic RCS of the passive RDA over an angle of from boresight, compared to the equal-size reference rectangular metallic sheet.

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A novel compact Ridge Substrate Integrated Waveguide (RSIW)-based hybrid ring coupler is hereby presented. The size miniaturization is accomplished through a twofold approach. First, the RSIW is used to reduce the coupler waveguide transverse dimension. The RSIW of the hybrid ring is then loaded by Electromagnetic Bandgap (EBG) structures, etched in its non-ridged broadwall, exploiting their slow wave effect to reduce the longitudinal dimension. It is demonstrated that the use of EBG-loaded RSIW can lead to a size reduction of more than 48% and 91% with respect to the unloaded RSIW and conventional SIW hybrid ring couplers, respectively.

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A novel reconfigurable defected ground structure (DGS) resonator fabricated on coplanar waveguide (CPW) technology is presented. The resonator is endowed with an original design which enables the generation of multiple transmission zeros at arbitrary frequencies. The chosen design is indeed based on a slot defect created on the lateral ground planes of the CPW with the double advantage to allow a simple reconfiguration, by means of surface mounted (or fabricated) components, and a very compact solution, by exploiting the transversal dimension of the coplanar wave transmission line (CPW-TL). Four different states of the diodes configuration are investigated, where in each state multiple transmission zeros are produced in the frequency range from 1 GHz to 11 GHz. The equivalent circuit of each state is obtained using a conventional circuit parameter extraction method. Moreover, the slotline design equations are used to identify the transmission zeros and validated using the magnetic field distribution inside the slot. In this work, the reconfigurability is first proven by means of short bridges mounted in specific locations. These bridges are then replaced by PIN diodes. Simulated and measured results are in good agreement.

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This paper addresses the characterization of Ba<sub>0.6</sub>Sr<sub>0.4</sub>TiO<sub>3</sub> dielectric properties on different dielectric substrates using three different components. First, for low frequencies, metal-insulator-metal (MIM) capacitors are used to determine the BST dielectric constant, loss tangent and tunability for different biasing voltages from 0-30 V showing a tunability range of 66%. For microwave frequency ranges, coplanar waveguides (CPW), and interdigital capacitors (IDCs) are investigated on silicon, R-plane sapphire (Al<sub>2</sub>O<sub>3</sub>) and magnesium oxide (MgO) substrates. CPW is used to determine the complex propagation constant, while IDCs are used to determine the BST voltage tunability from 0-55 V over 1-20 GHz. Sapphire and MgO introduce low loss tangent values of 0.03, while sapphire gives better tunability (20% at 18 GHz) than MgO (8.3% at 18 GHz).

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This paper presents a novel reconfigurable DGS cell on CPW. The structure consists of two independent ring resonators. A diode is used to connect and/or disconnect the second resonator, switching the structure from single band to multi-band resonance circuit. An equivalent circuit has been extracted from the simulated results representing the DGS in both states of the diode. EM simulation, equivalent circuit model and measured results show good agreement. Finally, design rules and considerations have been illustrated.

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This paper reports the DC and Radio Frequency (RF) characterization of Ba0.6S0.4TiO3 thin films using three different components. For DC characterization, two single circle patch MIM capacitors of different radii are fabricated over Pt/Ti/SiO2/Si substrate covered with a 350 nm BST film. The measurement results show a tunability range of 61% for 0V to 20V biasing voltage. For higher frequency characterization, another MIM structures consisting of two imbricate circle patches are fabricated on the same substrate, where BST intrinsic parameters are extracted using a differential method. Results show that BST dielectric constant is nearly frequency independent; giving a tunability of 53% up to 20 GHz. On the other hand, a reflection IDC fabricated on BST/Al2O3 substrate is investigated. The IDC exhibits a capacitance tunability of 20% at 18 GHz.

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This paper addresses the characterization of the ferroelectric Ba0.6Sr0.4TiO3 on different substrates using three different microwave components. First, at low frequencies, metal-insulator-metal (MIM) capacitors are used to investigate the variation of the BST dielectric constant and loss tangent for different biasing voltages. BST shows a variation for the dielectric constant from 380 to 130, recording a tunability range of 66 %, and loss tangent of 0.027 to 0.005. In the range of frequency from 1 to 40 GHz, coplanar waveguides (CPW) are used to investigate the effective dielectric constant of BST on four different substrates, HR silicon substrates covered by silicon dioxide, silicon covered by silicon dioxide and silicon nitride, magnesium oxide (MgO (100)), and R-plane sapphire (Al2O3) substrate, all covered with 350 nm BST layer. The effective dielectric constant over silicon substrates covered by silica and BST is 7.2, 6.3 for Al2O3 substrates and 5.8 for MgO; and for the loss tangent, Al2O3 and MgO give about 0.03, while silicon substrates suffer higher values of 0.08 to 0.25. Finally, to study the tunability of microwave structures on the investigated substrates, interdigital capacitors (IDC) are fabricated and measured for different biasing voltages ranging from 0 to 55 V. IDCs over MgO show a tunability of 8.3%, while IDCs over sapphire show 20%.

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In this paper, a novel reconfigurable bandpass filter based on defected ground structures has been presented. The filter consists of two basic elements. The first is the inductively coupled resonator giving the bandpass filter response, and the second is the novel DGS cell allowing reconfigurability and miniaturization. Simulated and measured results are in good agreement. The flexibility of the design in the different cases has also been demonstrated.

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A novel defected ground structure cell was presented. The cell was built on coplanar waveguide technology. Two diodes in each side of the ground planes allow us to switch the filter between different passbands. Simulated and measured responses were presented showing very good agreement. An electromagnetic explanation of the structure based on slot transmission line was also presented. The cell shows very promising features for the implementation of small and efficiently reconfigurable building block for filters. The very narrow stopbands in the responses may be enhanced by putting more cells in cascade. This work is a first step toward implementation of a silicon integrated reconfigurable filter using MEMS switches in place of diodes.

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This paper addresses DGS based inductively coupled bandpass filters fabricated on coplanar waveguide (CPW) technology. The addition of the DGS to the conventional inductively coupled resonator BPF allows the miniaturization of the resonator by exploiting the transversal dimensions of the CPW, while maintaining its performance with respect to insertion and return loss values. On the other hand, the DGS cell allows reconfiguration of the structure from a single band to a multiband BPF. The design procedure of the filters with the DGS is explained with filters designed at 5 GHz. Simulated and measured results show good agreement.

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This paper addresses a modified bandpass ring resonator filter providing compact size, low insertion-loss, wide bandwidth, sharp rejection and suppressed higher order modes. Typically, ring resonator filters suffer from large occupation area and limited out of band rejection. These limitations are tackled in this work by means of a threefold approach. On the one hand, the use of internal folded stubs allows the exploitation of the internal ring area yielding more than 70% of overall size reduction with respect to conventional orthogonal straight stubs solution. On the other hand, the introduction of Defected Ground Structures (DGS) and Uniplanar Compact-Photonic Bandgap (UC-PBG) structures, formed by etching patterns in the ground plane of the filter, enhances by great extends the rejection of higher order modes providing a stopband that reaches 4.7 GHz beside offering a further advantage in terms of size reduction. The two approaches are first separately validated and then simultaneously combined to provide an optimized filter design. Finally, a solution employing via holes to replace the tuning stubs is explored in order to extend the lower stopband. EM simulation, equivalent circuit model, as well as measurement results validate the followed design approach and are in excellent agreement within each other.

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This letter addresses a modified bandpass ring resonator filter providing compact size, low insertion-loss, wide bandwidth, sharp rejection, and suppressed higher order modes. It is demonstrated that the use of internal folded stubs translates into an overall size reduction of more than 70% through the exploitation of the internal ring area. The introduction of defected ground structures enhances the rejection of higher order modes beside offering a further advantage in terms of size reduction. It is furthermore shown that electromagnetic simulations, transmission line model, as well as measurement results are in very good agreement.

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This paper addresses a modified bandpass ring resonator filter providing compact size, low insertion-loss, wide bandwidth, sharp rejection and suppressed higher order modes. The filter enhancement follows a threefold approach. First, UC-PBG structures are used to suppress the higher order passbands yielding an upper stopband that reaches 4.7 GHz, beside offering a further advantage in terms of size reduction. Second, the use of internal folded stubs allows the exploitation of the internal area of the ring resonator, which translates into an overall size reduction of 84.5%. Finally, a solution employing via holes to replace the tuning stubs is explored in order to extend the lower stopband. EM simulation, equivalent circuit model, as well as measurement results validate the followed design approach and are in excellent agreement within each other.

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The main aim of this paper is the reduction of size of microstrip filters by using vias, while enhancing other filter properties such as insertion-loss and passband bandwidth. Two filters are presented. The first one is a new compact, low insertion-loss, sharp-rejection, wide-band bandpass filter which may be considered as a modification of the previously published bandpass filter using ring resonators. When replacing the two tuning stubs by two vias, the size of the filer is reduced up to 28% from its original size, while the achieved bandwidth is 95.8%. The filter also supports constant group delay along the passband of the filter. The second filter is the parallel-cascaded rectangular resonator filter. When adding two-vias, the filter is reduced to 75% of its original size. Then the same filter with two opposite vias was designed, showing that the opposite vias cause the same effect of asymmetric feed. Both filters are fabricated and the measured responses have good agreement with the simulated ones.